Khalil J. Asali,* Mohammad El-Khateeb
Department of Chemistry, Jordan University of Science and Technology,
P.O. Box 3030, Irbid 22110, JORDAN

Abstract
Reactions of M(CO)5THF, which was generated photochemically from M(CO)6 in THF, with tBu-SR (R = (CH2)4CH3, (CH2)5CH3; M = W, Cr) at room temperature afforded exclusively (CO)5M(tBu-SR) type complexes. These new complexes have been characterized by IR and elemental analysis. Ligand-substitution reactions of these complexes with tri(isopropyl)phosphite ( = L) in chlorobenzene ( = CB) solutions gave (CO)5M(P(O-i-Pr)3) as the sole reaction product.  A thermal kinetics study of these ligand-substitution reactions under pseudo-first-order conditions in CB solutions, confirmed that these reactions proceed via a mechanism which is first-order in substrate and zero-order in P(O-i-Pr)3 concentrations. Thus, a dissociative  mechanism is proposed, which  involves initial M-S bond breaking, followed by fast attack of the incoming nucleophile, L, at the resulting five-coordinate intermediate. Rate constants and activation parameters for these ligand substitution reactions have been determined and are discussed.
Keywords: Metal carbonyls, organic sulfide ligands, kinetics, mechanism.